"In NixOS, the entire operating system - the kernel, applications, system packages, configuration files, and so on - is built by the Nix package manager from a description in a purely functional build language. The fact that it's purely functional essentially means that building a new configuration cannot overwrite previous configurations. Most of the other features follow from this." Interesting approach. A Linux distribution, sure, but with some very refreshing ideas about system configuration.

The big problem from this approach (unless I missed something) is that updated dependencies are not picked up until you rebuild the package using them.

There's also the issue of disk space usage, but as long as you are prepared for it, it shouldn't matter.

All in all I like the concept (featured in OSNews in 2007), but it seems to throw in a lot of computer resources to get features that sound cool but are rarely needed, or achievable via simpler methods.